Known impact absorbers of the telescoping tube type generally function so that, in the case of a collision, the inner tube is forced into the outer tube or the outer tube is forced over the inner tube (or both) and an elastic material or the like within the tubes can be subjected to compression and is thus capable of generating a resistance to this telescoping shifting of the two tubes.
The elastic material, for example, can be received in the outer tube and can have the form of the inner tube or it can be received in partition between a partition or bulkhead and a wall of the tubes or in a sheath within the tubes.
An oil filling can also be provided for the tubes which may be displaced upon the telescoping contraction of the interfitted tubes.
A drawback of all of these earlier constructions is that, by and large, there is no constant resistance to the telescoping contraction of the tube assembly, but rather the resistance thereto progressively increases. In the case of an oil filling, where it is possible to provide a constant resistance, other problems arise, e.g. problems of sealing.
A constant resistance to the telescoping contraction of the tube assembly is desirable when the elastic spring stiffness of the vehicle chassis is to be fully utilized from the beginning of a collision process.